Nucleic acids, known today as deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are the fundamental molecules responsible for carrying the genetic instructions of life. These complex biopolymers store and transmit the hereditary blueprint for all cellular functions, making their discovery a landmark achievement in biological history. The identification of this previously unknown class of cellular components marked a transition point to understanding its intricate molecular machinery. This foundational work paved the way for modern molecular biology, genetics, and our current understanding of inheritance.
Friedrich Miescher: Identifying the Core Component
The initial identification of the substance now known as nucleic acid belongs to the Swiss physician and physiological chemist, Friedrich Miescher. Miescher had a focused academic interest in the chemical composition of individual, simple cells, a relatively new area of study in the late 1860s. After completing his medical studies, he dedicated himself to biochemical research. In the autumn of 1868, Miescher began working in the laboratory of Ernst Felix Hoppe-Seyler at the University of Tübingen in Germany. Hoppe-Seyler assigned Miescher the task of investigating the chemistry of white blood cells, or leucocytes, because they were relatively uncomplicated cells. This specific focus on the contents of the cell nucleus guided his experiments toward an entirely new chemical entity.
Miescher developed methods to isolate and analyze the components of these cells. By the beginning of 1869, his rigorous chemical analysis led to the isolation of a unique substance that was unlike any known protein or lipid. This discovery established him as the pioneer who first chemically isolated the core component of hereditary material.
The Source Material and the Substance: Isolating Nuclein
The material Miescher used for his isolation was unconventional, yet practical for the time. He obtained white blood cells from discarded surgical bandages collected from a nearby hospital in Tübingen. Since pus is rich in leucocytes, the bandages provided a consistently available source for his chemical investigations.
His experimental protocol began with washing the cells off the bandages and using salt solutions to purify the white blood cells. To analyze the contents of the cell nucleus, he employed the enzyme pepsin to strip away the surrounding cellular material. The substance that remained, resisting the pepsin digestion, was isolated from the cell nuclei.
Miescher characterized this precipitate using elemental analysis, revealing a high content of phosphorus, a feature distinct from proteins. Recognizing that he had found a novel chemical entity originating from the nucleus, he named the substance “Nuclein.” This term reflected its nuclear localization and its unique chemical resistance.
From Nuclein to Nucleic Acid: Refinement and Legacy
The substance Miescher called “Nuclein” was not immediately recognized for its biological significance, and its publication was delayed until 1871 due to the skepticism of his mentor, Hoppe-Seyler. Although Miescher continued his work, even finding a richer source in salmon sperm, the full chemical characterization of the molecule took decades. The next major step came in 1889, when the German pathologist Richard Altmann further purified the substance. Altmann demonstrated the material possessed strongly acidic properties and officially coined the more chemically descriptive term “nucleic acid” to replace Miescher’s original name.
Subsequent research established that nucleic acids existed in two distinct forms: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). While the function of nucleic acids remained a mystery for many years, the later realization that they, and not proteins, were the carriers of genetic information cemented Miescher’s initial isolation as the seminal event in the history of molecular biology.